Background/Purpose:

Anti-beta2 glycoprotein I (GPI) is not part of the ACR classification criteria for SLE, and IgA isotypes are omitted from the classification criteria for APS. We studied the prevalence and associations of anti-beta2 glycoprotein I IgA in a large multi-center study.

Methods:

The dataset consisted of 1384 patients with both anti-beta2-GPI IgA measured and a consensus physicians diagnosis (657 with SLE and 727 controls with other rheumatologic diseases). Of the 657 SLE patients, 599 (91%) were female, 394 (60%) were Caucasian, 134 (20%) were of African descent, and 76 (12%) were Asian. Their mean age (years) was 37.9±13.3. P-values were calculated based on the chi-square test (SAS Institute, Cary, NC, USA).

Table 3: Sensitivity and Specificity for SLE, based on Anti-beta2 Glycoprotein I IgA Positivity

Sensitivity %

Specificity %

Anti-beta2-GPI IgA

14.3

93.3

Conclusion:

Anti-beta2 glycoprotein I IgA was more prevalent in SLE patients (14%) than in patients with other rheumatologic diseases (7%) in this international multi-center study. It can occur as the sole isotype of anti-beta2-GPI in SLE. It was strongly associated with age, anti-dsDNA and other antiphospholipid antibodies and was highly specific for SLE. This was the rationale to include anti-beta2 glycoprotein I IgA in the new SLICC classification criteria for SLE.